Lock stitch sewing machine



Jan. 29, 1952 c. R. BACZKLIN 2,583,538

LOCK STITCH SEWING MACHINE 7 Filed Oct. 19, 1949 3nnentor Clare/we Back /11 Gttornegs Patented Jan. 29, 1952 I LOOK STITCH SEWING MACHINE Clarence R. Backlin, Floral Park, N. Y., assignor to Willcox & Gibbs Sewing Machine Company, New York, N. Y., a corporation of New York Application October 19, 1949, Serial No. 122,285

This invention relates to lock-stitch sewing machines, and more particularly to a lock-stitch machine of the type having a rotary hook with an open-sided raceway for the bobbin case, and having a full-floating bobbin case.

An object of the invention isto provide an improved lock-stitch machine of the above type, which is able to sew faster, that is, at higher speeds, than prior machines.

Another object of the invention is to provide an improved high speed lock-stitch machine as characterized above, which will sew more material before the bobbin becomes empty and requires replacement.

Essentially the speed of a sewing machine depends on the speed of the parts handling the thread, and the speed which can be imparted to the thread by these parts. Included in the parts which carry out critical thread-handling operations in a lock-stitch machine of the above type are the rotary hook, bobbin case, and the hanger for the latter, and the present invention is particularly concerned with improvements in these a parts to enable the machine speed and thread capacity to be materially increased.

Heretofore, lock-stitch machines having fullfloating bobbin cases employed a 3 to 1 ratio between the main shaft and the rotary hook. In these machines it was required to have a narrow gap ahead of the hook point in order to provide as, much bearing or raceway surface in the hook for engagement by the segmental bearings on the bobbin case which are necessary to produce the full floating movement of the case. If it was attempted to use a wide gap, the bearing on the top of the'hook would be decreased and the case would wedge and jam in the gap.

In such machines due to the impossibility of providing a wide gap in the hook ahead of the point, the encirclement of the bobbin case by the needle thread loop and separation of the loop from the bobbin case required at least one revolution of the sewing hook, this taking place under considerable speed when the machine is operating normally. For example, at a machine speed of 3400 R. P. M. the time which the needle thread loop is given, to encircle and leave the bobbin case, is on the order of /110 of a second, due to the fact that the hook speed is 10,200 R. P. M. If such a machine is speeded up to 5,000 R. P. M. the hook speed becomes 15,000 E. P. M. and the time available for the needle thread loop to encircle and leave the bobbin case becomes /250 of a second. With the terrific speeds and short time intervals encountered when 7 Claims. (Cl. 112-231) the machine speed is 5,000 R. P. M. the control of the sewing or stitching could not always be satisfactorily accomplished for all practical purposes because of difficulty in passing the loop in such a short time.

According to the present invention the above T objects, i. e. faster machine speeds and greater thread capacity in the bobbin, are accomplished by changing the ratio of the machine to 2 to 1, so that the hook speed is only double that of the machine, solving the loop-passing problem, and by providing a novel hook, bobbin case and hanger structure whereby the needle: thread loop is caused to leave the bobbin case, after encirclement thereof, sooner in the loop-passing cycle and whereby an improved balance and control means for a larger and heavier bobbin case is effected to prevent interference with the needle thread loop when it is encircling the bobbin case.

I have found that when a 3 to 1 ratio machine is changed to a 2 to 1 ratio, the time allotted to the needle thread loop to encircle and leave the to 1 ratio machine.

time for one revolution becomes /1113 of a second. Therefore this fraction of a second is the time given for the needle thread loop to encircle and leave the bobbin case, and is substantially longer than the /170 of a second interval in a 3 However, whereas a 3 to l ratio machine provides /85 of a second for the take up of the needle thread loop, the 2 to 1 ratio machine provides only 1/113 of a second for the take-up mechanism, at machine speeds of 3400 R. P. M.

I In accordance with the present invention I have devised a novel hook and bobbin case structure whereby the needle thread loop is caused to leave the bobbin case sooner than was heretofore possible. Thus I can reduce the time allotted to the operation of encircling the bobbin case by the needle thread loop, and can increase the time allotted for the take-up operation. I have found that since the changing of the machine ratio provides an excess over the amount of time required to encircle the bobbin case by the needle thread loop, this altering of the relative times. which I have accomplished provides an ideal solution to the problem and enables much higher machine speeds to be attained with satisfactory sewing characteristics. For example, at a machine speed of 5,000 R. P. M. one revolution of the hook at a hook speed of 10,000 R. P. M. occurs in 1/666 of a second, and this may be compared with the 1/170 of a second interval in a 3 to 1 ratio machine operating at a satisfactory sewing speed of 3400 R. P. M. I- findfthatwith my improved hook, bobbin case, and hanger construction I can satisfactorily operate a 2 to 1 ratio machine at a speed of 5,000 R. P. M., this being accomplished mainly by proper allocation or division of the time interval oil/s4 of a second represented by two revo1utionsof-thehookj'be tween the loop passing operation ahd the ta e- 11 operation. I

In the specific embodiment ot the invention illustrated herein, I provide a cut-away portion on the rim of the hook raceway, extending fora distance ahead of the'fhook point, and provide a sec'ond'cut away portion in thehpper'fian'ge' sec- 'jti'on of thebobbincase,adapted'tocooperate with the'cut-aw'ay part" of the hook whereby f during part of each'revolution' of 'the'ho'ok asimulated wide gap exists between the "upper portions of "the hook andth'ejbobbincaseyresultingiri the nee'dlethread 'loopp'assing out through-this wide gap at a time'relatively early in'the sewing cycle j and" s'ubstantiallydn advance of the hook completing'"'onerevolution in said cycle. This novel v means of "providinga so calledwide gap in hook, does "not reduce -thenecessary bearing surface for" thefloating case as'explained'earlier. It

" does" however reduce the width of "the bearing surface but as'the' bearing flanges onthebobbin case aremadeproportionately wide; said reductionhas no illefiect.

' As a'consequen'ce ofthe greater time allowed for the needle thread "loop to "encircle the bobbin case even when this time is thus shortened, the

" sewingfunction of'the hook and bobbin case is made "less critical; and consequently a" larger bobbin case may be usedpanda larger bobbin havinga substantially increased "thread capacity.

"Since the bobbin case is of thfull floatingtype,"

this change willnot" materially increase "friction -'-or-vvear t The incre'a'se' in-thread "capacity may; be as great as 45; to 50 per centover'the-'capacity--here- "-tof-ore considered the maximum in a 3- to 1-ratio 5Q machine. To eliminate interference'wvith the needle thread loop' during its "movement in encircling the" larger and heavier-hobbit? case, I provide an improved control and-bearing means between the bobbin' case and the hanger therefor;

to cause the swing or oscillation' of thebobbin -case to be out of a vertical-line and more in a horizontal plane; In efiecting-this, l provide a land -or bearing surface at-the lower" portion of the bobbin case-for engagementwith the bobbin case hanger, which land is offset 'orlocatedto one' sideof; a vertical center line passing through the bobbincase. A similar offset/land 'or bearing surfaceis provided "at 'the upper portion of *the bobbin'case wh-ich islocated on the opposite;

sideof the verticalcen'ter line. I have foundthat these oifset lands prevent swinging movement of the bobbin case about a purely verticalaxis,

and instead cause-a swinging of thecase about an axis disposed at a wide angleto the vertical, thereby resulting in less tendencyto pin'ch' the needle. thread'loop' between the bottom portions "of the bobbin case and the hanger.

Inconjunction with the above structure I providean improved'needle shield in'the 'bobbinease 4 which prevents inadvertent striking of the needle by the hook point and consequent damage to these parts, and this is an important feature of the invention. 5 Other features and advantages will hereinafter appear.

} In the accompanying drawings: Figurei l is aside elevational view of the im- ""provedhook, bobbin caseandhanger' structure .10 of this invention mounted in a sewing machine, a portion of the machine bed being shown in vertical section.

Fig. 2 is a top or plan view of the hook, bobbin case'andhajngefof- Fig. l. 5 Figj3is an'elevational view of the outer side of the" bbbbinc'ase of this invention, and

-FigJ 4 iskan -end elevational view of the rotary hook.

Fig: 5 is a section taken along line 55 01' zc r. V

Referring to Fig. lathe present improved novel, high peed hook; bobbin case and hanger struc- *ehinenr operative position" below a cloth plate H. A hook shaft l2'is journaled-in the bed I and at its p'r'otrudingend mounts a hub .l3carrying "a-"jrotary hook I 2 which is in the form of a 1 relativelyshallow c'up. 1

The hook it is of the-open raceway-'typer' that is, it has 'an annularwall portion constituting a cir'cul'ar raeeway which'is open at the side.'* As shownin- Figs, I and 4 the :hook M has a hook 'properorpoint I 6 adjacent anangularly disposed thread slot I1, the latter extending inside of a u'rved shield' 'lswhich is secured to'the exterior the hook wall 15. -Tn'side the rotary hook l4 a bobbin' case" 19 '-is loos"ely carried," the said case being' heldin 'operative' position' bya hanger M -having a shank 2| which-is secured to ahanger arm 22 pivotally =-connected with a'hanger bracket 23 attached to the' underside ofthe bed I0. The bobbin "case 19h'as a loop check notch 24 in itstupper portion, w hich loosely receivesa loop check or projection 25 on theh'anger '20. As is-welhmderstood, engagement'between the'loopcheck 25 and the -"wall 26 'of' the loop'eheck notch 24 prevents the bobbin case 'i9"-from turning when the rotary hook Hi-is operating.

ns abovementioned I have 'found that materially:greatermachine:speeds may be attained with satisfactbry sewing, when the present improved hook, *b'obbin'case' and hanger structure re incorporated in a 2 to 1 ratio machinej'wheren the rotary hook makes two revolutions for'each revolution of the-main machine shaft.

In accordance i'withthe present invention the hook 4, bobbincase i9 and hanger"20 are so constit'uted that= the needle I thread =1o0p .vvhen" encircling the bobbin case leaves the latter very soon in*the-'sewing cyclefprior to'the hook -passing through onewompleterevolution (which occurs n" one'half"=of=saidicyc'le). 5 Thus more time available for the take-up"mechanism of the b achineto pull'the p tight; Alsogby the org anizatiorr'w'hich Iha've provided; there is no in- -terferencewith the needle thread loop as the la tter is' passedaround the bobbin ease at high speeds. Therfefore the loop -will notonly be '9 qiiickly"s'eparatedfronithe'=- bobbin case} but it -'will n'ot be' delayed or hampered inits travel 1 =-around the'casei and as a consequence,- satisfactory sewing at -=re1atively' --high speeds may'flbe i v e ft m s In-"accomplishingthis;referring to Figswl; 2

and 4, I cut back an edge portion of the raceway I of the hook, at a location immediately ahead of the hook point, to provide a peripherally-extendingelongate relatively narrow indentation 21 in the rim of the hook, the said indentation extending between the two radial dot-and-dash lines 28 and 29 shown in Fig. 4. The anglebetween the radial lines 28 and 29 is approximatelylZO", indicating that the indentation extendsabout one-third of the way around the periphery or rim of the hook l4.

As shown in Fig. 2, I also provide a second indentation 30 in the upper portion of the bobbin case l9, by cutting awayparts of a flange section 3| of said bobbin case forming the segmental bearings therefor. The remaining uncut or end portions of the flange section 3! are adapted to engage a circular shoulder32 located on the inside of the raceway l5 of the hook M. The cutting away of the flange section 3! thus provides clearance or space without reducing the bearing for the casing engaging at the shoulder 32.

The indentations 21 and 30 are so located that prior to the hook point H; of the rotary hook reaching its uppermost position wherein it takes off the needle thread, the indentations will be alongside of each other, and will cause a simulated wide gap to exist between the hook and bobbin case at these points while retaining requisite bearing engagement. This wide gap enables the needle thread loop to leave the bobbin case very quickly after it has encircled the same, and

therefore gives the take-up mechanism of the sawing machine more time to take up or pull the loop tight. This is extremely important for the reason that in a 2 to 1 ratio machine where the rotary hook M will rotate twice as fast as the main machine spindle, the time during which the take-up mechanism may act is considerably reduced over that provided in a 3 to 1 ratio machine, where encirclement of the bobbin case occurs in a much lesser time. It will be understood that if encirclement of the bobbin case occurs in the first revolution of the sewing hook, in the sewing cycle, there remains in a 3 to 1 ratio machine two revolutions of the hook during which the take-up of the loop would be accomplished. In a 2 to 1 ratio machine, if encirclement occurs in the first revolution of the hook, there remains only one other revolution of the hook during which the take-up of the loop may be effected. Thus the matter of having the loop leave the bobbin case very quickly after the encirclement of the case is of extreme importance in providing additional time for the take-up mechanism to act.

Where a 2 to 1 ratio is employed between the hook and the main shaft of the sewing machine, the hook speed for any given machine speed will be much less than where a 3 to 1 ratio is employed. Therefore with this lesser speed the sewing function involving the encirclement of the bobbin case by the needle thread loop is not so critical. As a consequence, the size and weight of the bobbin case may be increasedflenabling the use of a larger bobbin holding more thread, and this is an important advantage where a machine is to be run at higher speeds, since in terms of elapsed time it means that empty bobbins will not have to be replaced by full bobbins so frequently.

However, when a larger or wider bobbin and a heavier case are used to provide more thread capacity, the balance of the case is upset. The matter of proper balance and suspension-of the case is extremely important, since an improper balance will result in interference with the needle thread loop as it encircles the case.

i In accordance with the present invention I provide an improved means for balancing and controlling the movements of the bobbin case during the sewing operation whereby heat and friction are minimized, and whereby no interference is met by the needle thread loop during its encirclement of the case at high sewing speeds. To accomplish this result the bobbin case l9 must be suspended in the hook l4 to be full floating during the operation of these parts, and I arrange the bearing means for the case so that its swin ing or oscillating movements are about a nonvertical axis. Accordingly, referring to Figs. 2

and 3, I ofiset the loop check 25 from the center a slight amount. and also the loop check notch 24 which receives the loop check. The amount of offset is such as to bring the other wall 33 of the notch 24 almost directly under the needle hole 34 in the cloth plate II, this positioning enabling the bobbin thread 35 which passes upward inside of, and in engagement with, said wall to extend vertically to the center of the needle hole.

As clearly shown in Fig. 3 the bobbin thread 35 passes inside of a self-threader hook 36 through notch 36a from a tension spring 31 car ried on the exterior of the bobbin case.

The notch, as shown in Fig. 5, is lower than the edge 36b of the hook 36, the hook tapering to this 'edge so that as a thread in the notch is drawn upwardly across the face of the case it automatically engages the tapered face 360 and moves under the hook 36 to the space therebehind whereupon it snaps into overlying relation as shown in Fig. 3.

By the above location of the wall 33 of the loop check notch 24 the bobbin case I9 is suspended from the thread 35 substantially vertically below the needle hole 34 of the cloth plate.

In conjunction with the above suspension of the bobbin case below the needle hole, a bottom case stop 38 is provided on the lower portion of the case, Fig. 3, the said stop being in the form of a raised portion or land extending in a circumferential direction and disposedmainly to one side of the vertical central transverse plane of the bobbin case. In other words, the land 38 is disposed substantially wholly to the left of the vertical center line 39 (Fig. 3) which passes through the axis of the case and through the inside surface of the wall 33 of the loop check notch 24. The land 38 is adapted to engage the lower portion of the hanger 20 as shown in Fig. 1, the upper portion of the hanger 21!! extending below and engaging a curved shoulder 40 of the bobbin case to support the latter in suspension when the machine is at a standstill and the parts are not operative.

The offset position of the land 38 as provided by the present invention is extremely important in enabling high machine speeds to be attained in that it provides a control over the tilting movement of the bobbin case when the latter is suspended from the bobbin thread 35 which control results in the needle thread loop meeting with no interference as it is passed around the bobbin case by the rotary hook. In its suspended state, during the operation of the sewing machine, the bobbin case I!) tilts and oscillates within a very restricted path, and the offset/position of the land 38 causes the bobbin case to tilt or swing about an axis other than vertical. This minimizes any tendency for pinching of the needle thread loop between vthedowerrnost portionszoi thezhanger- 2.0. and the bobbin; case 19.

prevents, engagement between. said land and the upper portion of the hanger 20. The land 42 however may engage the upper portion of the hanger 20, audit will be obvious thatthis land is-practically diametrically opposite theland 4B andis; wholly to the right of the center line 39 of thelbobbin case. The combinedefiect of the lands '38 and 1 48 in conjunction with the suspension provided by the bobbin thread 35 results in .-the bobbincase l9 having a swinging movement about, an aixswhioh is noncoincidental with the vertical center line 39 shown in Fig. 3, and therefore the lower land 38 of the bobbin case, will not be in engagement with the lower party of the hanger 20 except for extremely limited periods of time. Thus the needle thread loop, may readily pass between the land 38 and the lower portion of the hanger 20 with practically no interlerence which might adversely affect the sewing operations of the machine. I have therefore provided by'the above organization in a 2-to lratio lock-stitch machine, a full floating bobbin case which in its action readily enables the needle thread loop to encircle the case without difficulty at relatively high sewing The remainin wall 43 of the flange section 3 1 may-beadvantageonsly employed in conjunction with a sloping surface 44 in the bobbin case IE! to act as a guide for the needle of the machine whenthe latter is extended through the cloth plate II. This guide prevents the needle from being struck by the hook point l6 of the rotary .hook, and prevents consequent damage to the needle and hook. p

A, second shield is provided for the needle of the machine, indicatedat 45. in Fig. 2, the said shield constituting the center wall of the loop check notch 24 of the bobbin case.

Variations and modifications may be made within the scope of the claims and portions of the improvements may be used without others.

I'claim:

1. In .a sewing machine having a rotary hook provided with an open-sided raceway, and having a bobbin case in said raceway-provided with a loop-Icheck notch and with a flangesection extendingpast-said notch and alon the periphery tion on its inner side whereby for part of a revolution of said hook prior to the hook point reaching its pick-d position a wide gap exists between the hook raceway and the bobbin case to enable the needle thread loop to leave the bobbin case relatively soon in each sewing cycle of the machine.

2.;In a sewingmachine having a rotary hook provided with an open-sided raceway, and having a. bobbin case in said raceway providedwith a flangesection extendingalong the top peripheral portion of the case to guide the same in said raceway, the improvement which comprises: the 2 edge of said raceway ahead of the hook being, cut

back o p ov de n on r a i el re indentation extending peripherally through j an arc greatersthan 90, and said flange section of the casebeingvcnt away. to, provide a second peripheral1yextending, elongate, relatively narrow indentation; on its inner side wherebyfor part of arevolution of said hook prior to the hook point reaching its pick-off position a wide gap exists between the, hookraceway and the bobbin case to enablethe needle thread loop to leave the bobbin case relatively soon in each sewing cycle ofithermachine 3. Ina-sewing machine having a rotary. hook geared to twice the machine speed'and Provided an openg-sided raceway and a shoulder therein, and haying abobbin case in said raceway provided with .a peripherally-extended flange along its 2012 for en agement, with said shoulder toiguide the. ease in the raceway, the improvement which part of a revolution of said hook prior to the hook point reaching its pick-off position a wide gapexists between the'hook raceway and the bob,- 7

bin case teen-able the needle thread loop toleave the bobbin case relatively soon in each sewing cycle of the machine.

4. In a sewing machine'having, a. rotary hook provided with anopen-sidedracewa'y, and having a; bobbin case in said raceway provided with a flange section extending along the top peripheral portion of thei case to guide the same in said raceway 'the improvement which comprises: the edge ofsaid race-wayahead of the hook being cut back to provide a peripherally extending, elongate, relatively narrow indentation, and said flange section of the case being cut away to provide a second peripherally extending, elongate, relatively narrow indentation on its inner side whereby for'part of a revolution of said hook prior to the hook point reaching its pick-off position a -wide,gap exists between the hook race.- way and the bobbin case to enable the needle thread loop to leave the bobbin case relatively hook-adjacent the notch, said hook tapering to an inwardly facing edge located in a plane above the bottom of, the notch and engaging a thread extendingirom the notch as the thread is moved upwardly across the case to automatically pick up andguide the thread to the rear of the hook and into threaded relation therewith.

6 In a -sewing-machine having a rotary hook provided with a wall forming an open-side raceway,:and; having a bobbin case in said raceway provided with a flangelsection extending along the top peripheral portion of the case to guide the same in'said raceway, the improvement which comprises: the edge of the wall forming said raceway ahead of the hook being cut away to provide a peripherally extendingelongate, relatively-nar row indentation less than'the depth of said flange V .7 section, and said flange section'of; the case being parti all y cutaway on theinner side centrally thereof to provide a second peripherally extending, elongate, relatively narrow indentation whereby for part of a revolution of said hook prior to the hook point reaching its pick-off position, said cut away portions overlap and form a wide gap between the hook raceway and the bobbin case to enable the needle thread loop to leave the bobbin case relatively soon in each sewing cycle of the machine.

'7. In a sewing machine having a rotary hook provided with a wall forming an open-side raceway, and having a bobbin case positioned in said hook for movement transversely of the axis of the hook and floatingly supported in said raceway by a hanger when the needle thread is free to take-up tension, said casing being provided with a flange section extending at least along the top peripheral portion of the case to guide the same in said raceway, the improvement which comprises having the edge of the wall forming said raceway ahead of the hook cut away to provide a peripherally extending, elongate, relatively narrow indentation less than the depth of said flange section, and having said flange section of the case partially cut away on the inner side centrally thereof to provide a second peripherally extending, elongate, relatively narrow indentation, said cut away portions overlapping and 10 forming a wide gap between the hook raceway and the bobbin case for part of a revolution of said hook prior to the hook point reaching its pick-01f position and while the casing is supported on the hanger to enable the needle thread loop to leave the bobbin case relatively soon in each sewing cycle of the machine, said flange and raceway providing bearing means therebetween when the bobbin case is lifted from the hanger by the take-up tension in the needle thread during a subsequent part of the revolution of said hook.

CLARENCE R. BACKLIN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 944,740 Madison Dec, 28, 1909 1,786,944 Hem1eb Dec, 30, 1930 2,495,637 Joseph Jan. 24, 1950 FOREIGN PATENTS Number Country Date 807,612 France Oct. 19, 1936 

